210 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



more clearly than others, but because he has deliberately brought it 

 into practice and thereby achieved a striking scientific success. Let 

 us hear him speaking of the crux of his theory — the idea of the simul- 

 taneity of events occurring at different places. 



The concept [of simultaneity] does not exist for the physicist until he has the 

 possibility of discovering whether or not it is fulfiUed in an actual case. We 

 thus require a definition of simultaneity such that this definition supplies us with 

 the method by means of which, in the present case, he can decide by experiment 

 whether or not both the lightning strokes occurred simultaneously. As long as 

 this requirement is not satisfied, I allow myself to be deceived as a physicist 

 (and of course the same applies if I am not a physicist), when I imagine that I am 

 able to attach a meaning to the statement of simultaneity. (I would ask the 

 reader not to proceed farther until he is fully convinced on this point) .' 



I think that if this statement had been made at any time in the 

 history of modern science, but had not been applied to the foundations 

 oi physical conceptions, it would have aroused no comment. Einstein 

 would have been regarded as simply saying that if our definition of 

 simultaneity is such that it is essentially impossible to determine 

 whether events are simultaneous or not, then it must be wrong; and 

 everyone would have agreed and turned to more important matters. 

 But he went further. He gave a definition which both accorded with 

 scientific practice and satisfied the requirement he had stated, and 

 then went on to show that certain modifications of our generally ac- 

 cepted notions of space and time must necessarily follow. This put 

 the fat into the fire, and instead of being ignored for saying the obvious, 

 he was railed at for saying the absurd. Philosophers in particular 

 were aroused, and when they realized that a mere empiricist was ven- 

 turing to challenge their fundamental principles in tones which re- 

 sounded throughout the world, they proceeded to administer the re- 

 buke which the occasion demanded. Here, for example, is a comment 

 by M. Jacques Maritain, the well-known French Catholic philosopher, 

 on the passage I have quoted (in which, it will be remembered, Ein- 

 stein asks the reader who is not convinced of his principle to read no 

 farther): 



Let us, then, obey our author and read no farther, for this little parenthesis 

 "the same applies if I am not a physicist," is of direct concern to us who have not 

 the honor to be physicists, and it presumes to introduce us into the most fallacious 

 metaphysics. * * * It is a fault so obvious to the eyes of a philosopher to 

 confuse the meaning of a concept * * * with the use which may be made of 

 the concept in this or that field of study, and more particularly to confuse a thing 

 * * * with the measure which we take of it by our senses and our instruments, 

 that we hesitate to impute such a mistake to anyone, whoever he may be. Every- 

 thing goes to show, however, that Einstein has made this mistake. 4 



(We may remark in passing that in speaking of measures, Maritain 

 has somewhat confused the issue; measurement is not mentioned by 



' The theory of relativity, English translation, p. 22, 1920. 



* Reflexions sur l'Intelligonce et sur sa Vie Propre, pp. 205-6, 1926. 



